1. Field of Invention
The invention relates to a stitch data compensation device which corrects a relative amount of X- or Y-axis movement of a work cloth with regard to a needle.
2. Description of Related Art
Some sewing machines use an actuator that is controlled based on an amount of sewing data movement in the X- or Y-direction, thereby moving a work cloth in the X- or Y-direction. In this case, when the work cloth is moved in the opposite direction, backlash occurs in the transmission mechanism which transmits a driving force of the actuator to the work cloth, and an actual movement amount of the work cloth is insufficient for the sewing data. Therefore, when the work cloth is moved in the opposite direction, the movement amount in the X- or Y-direction needs to be corrected in order to cover the insufficiency.
To cope with the insufficiency of the mechanical movement that is generated when the work cloth is moved in the opposite direction, a predetermined value is added to the sewing data. However, if the predetermined value to be added to the sewing data is greatly over the insufficiency, the finished sewing pattern may have a distorted shape. For example, when the shrinkage of the work cloth due to a thread tension during sewing can not be prevented, gaps can be seen in the finished satin pattern. In a fill pattern, stitches will be jagged because needle penetration points are not aligned. Moreover, when the running stitching is used and the direction of the running stitching is reversed, stitches to be made on the return may deviate from the ones already made in the original movement direction.
Japanese laid-open Patent Publication No. 4-259484 discloses a frame feed correction device for an embroidering machine, in which the frame feed correction data can be set for X- and Y-axes separately. According to this device, the feed amount can be corrected in consideration of not only the backlash in the transmission mechanism but also the shrinkage of the work cloth.
However, the shrinkage of the work cloth varies with the degree of the angle to be formed by successive two stitches. The correction device described in the Japanese laid-open Patent Publication No. 4-259484, is incapable of accounting for the shrinkage effect caused by the angle formed by successive stitches and to correct the stitch data to compensate for that effect. Namely, when the angle between stitches is smaller, the forces to be exerted on the stitches are combined into a large force, which can pull the work cloth greatly, and the resultant shrinkage will be great. On the contrary, when the angle is greater, the force to be combined will be smaller, and the cloth will be tensed with a little force and the shrinkage will be smaller. However, in the correction device, it is impossible to correct stitch data properly for every single stitch in consideration of various conditions like the angle between stitches and the tendency for shrinkage which differs according to types of the cloth.